When Size Really Does Matter- The Pearson 9-Foot Single.

Updated: 26 May 2003
Back to Home PageBack to The Loco Index

J Pearson was locomotive superintendent of the Bristol & Exeter Railway, and designed this 4-2-4 express tank engine, eight of which were built in 1853-54 by Rothwell of Bolton. (The B&E later became part of the GWR)

The dominant feature is of course the enormous 9-foot diameter driving wheel, which was flangeless. Surprisingly, this is not a record: details to follow. The whole engine looks big because it is a broad-gauge (7-foot) locomotive; the broad gauge was abolished in May 1892. Weight was 42 tons with the tanks full. Boiler pressure is unknown.

Above: The Pearson 9-Foot single of 1853, bearing a magnificent tuba-like chimney. Arrow shows boiler bracket.

Several other features of this engine's design have attracted comment; for example the smokebox was unusually short, and the ends of the cylinders can be seen protruding ahead of it. The suspension for the enormous driver was a peculiar arrangement of four india-rubber discs, on each side of each wheel. The outside cylinder containing these discs can be seen just above the axle. The wheel load was then transferred via frighteningly thin vertical rods (in compression!) to the large bracket riveted to the top of the boiler; (arrowed) the boiler in turn passed the load to the inside frames. This seems a very doubtful arrangement, but we may never know if it gave trouble as records of this design's performance do not seem to exist.

Above: The Pearson 9-Foot single portrayed in rather better photographic quality, but without the human figures that show just how big it was.

These locomotives had an average life of only sixteen years, which seems to show that they left a lot to be desired. Very possibly there was insufficent adhesion weight- after all, only one out of five axles was driving. All eight were scrapped between 1868 and 1873.

Sectional illustrations of these engines are to be found in The Engineer supplement for Dec 16, 1910. Run, don't walk, to the nearest library.

Back to Home PageBack to The Museum EntranceBack to The Loco IndexTop of this page